Synopsis

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Step 2

What command(s) is this example for ?

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When the command runs, it will hand off its output to sendmail
for delivery to the specified recipient, and in the quick test
I've just run, this does work.

Of course, if you're already redirecting the output from
some-command to go somewhere else, you might be out of luck --
but, then, you could always tee(1) the output, or add a final
line to the at job calling sendmail to push out the message.

Puzzle of atrm vs at -d

Program code can know what the name of the executable was that
launched it. It's possible that the at program does
something like this:

if (my name is 'atrm') then
add '-d' parmeter
end
do stuff like regular 'at' program.

description

at and
batch read commands from standard input or a
specified file which are to be executed at a later time,
using /bin/sh.

at

executes commands at a specified time.

atq

lists the user’s pending jobs, unless the user is
the superuser; in that case, everybody’s jobs are
listed. The format of the output lines (one for each job)
is: Job number, date, hour, queue, and username.

atrm

deletes jobs, identified by their job number.

batch

executes commands when system load levels permit; in
other words, when the load average drops below 1.5, or the
value specified in the invocation of atd.

At
allows fairly complex time specifications, extending the
POSIX.2 standard. It accepts times of the form HH:MM
to run a job at a specific time of day. (If that time is
already past, the next day is assumed.) You may also specify
midnight, noon, or teatime (4pm) and you can
have a time-of-day suffixed with AM or PM for
running in the morning or the evening. You can also say what
day the job will be run, by giving a date in the form
month-name day with an optional year, or
giving a date of the form MMDD[CC]YY,
MM/DD/[CC]YY,
DD.MM.[CC]YY or
[CC]YY-MM-DD. The specification
of a date must follow the specification of the time
of day. You can also give times like now +count
time-units, where the time-units can be minutes,
hours, days, or weeks and you can tell at
to run the job today by suffixing the time with today
and to run the job tomorrow by suffixing the time with
tomorrow.

For example, to
run a job at 4pm three days from now, you would do at 4pm
+ 3 days, to run a job at 10:00am on July 31, you would
do at 10am Jul 31 and to run a job at 1am tomorrow,
you would do at 1am tomorrow.

The definition
of the time specification can be found in
/usr/share/doc/at/timespec.

For both
at and batch, commands are read from standard
input or the file specified with the -f option and
executed. The working directory, the environment (except for
the variables BASH_VERSINFO, DISPLAY,
EUID, GROUPS, SHELLOPTS, TERM,
UID, and _) and the umask are retained from
the time of invocation.

As at is
currently implemented as a setuid program, other environment
variables (e.g. LD_LIBRARY_PATH or LD_PRELOAD)
are also not exported. This may change in the future. As a
workaround, set these variables explicitly in your job.

An at
- or batch - command invoked from a
su(1) shell will retain the current userid. The user
will be mailed standard error and standard output from his
commands, if any. Mail will be sent using the command
/usr/sbin/sendmail. If at is executed from a
su(1) shell, the owner of the login shell will
receive the mail.

The superuser
may use these commands in any case. For other users,
permission to use at is determined by the files
/etc/at.allow and /etc/at.deny. See
at.allow(5) for details.

options

-V

prints the version number to
standard error and exit successfully.

-qqueue

uses the specified queue. A
queue designation consists of a single letter; valid queue
designations range from a to z and A to
Z. The a queue is the default for at
and the b queue for batch. Queues with higher
letters run with increased niceness. The special queue
"=" is reserved for jobs which are currently
running.

If a job is
submitted to a queue designated with an uppercase letter,
the job is treated as if it were submitted to batch at the
time of the job. Once the time is reached, the batch
processing rules with respect to load average apply. If
atq is given a specific queue, it will only show jobs
pending in that queue.

-m

Send mail to the user when the job has completed even if
there was no output.

files

The correct
operation of batch for Linux depends on the presence
of a proc- type directory mounted on
/proc.

If the file
/var/run/utmp is not available or corrupted, or if
the user is not logged on at the time at is invoked,
the mail is sent to the userid found in the environment
variable LOGNAME. If that is undefined or empty, the
current userid is assumed.

At and
batch as presently implemented are not suitable when
users are competing for resources. If this is the case for
your site, you might want to consider another batch system,
such as nqs.